1. Field of the Invention
The present invention relates to semiconductor thyristor devices and, more particularly, to a gate turn-off thyristor incorporating an insulated gate turn-on controlling transistor (MAGTO thyristor).
2. Description of the Related Art
In a conventional gate turn-off thyristor capable of self turn-off (known as a "GTO thyristor"), a control electrode is provided on a P type base layer to turn off the thyristor by partially discharging an anode current from the electrode as a base current. Typically, such a control electrode comprises elongated conductive layers alternately arranged between and parallel to parallel elongated thyristor gate electrode layers on a substrate.
With such a structure, however, the wiring resistance of the control electrode cannot be minimized as required. This degrades the efficiency of outflow of the base current from the electrode in the turn-off mode of the thyristor, thereby reducing the turn-off rate of the thyristor. In addition, if the control electrode is micropatterned to have a reduced electrode width (although an interval between neighboring gate electrodes is not much reduced even if the control electrode width is reduced) in accordance with increasing needs for high integration density, the turn-off operation is delayed at an end portion of the control electrode. As a result, in the worst case, the anode current is locally concentrated so as to destroy the device.